Recently, the greenhouse effect by CO2 has been pointed out as one of the causes of the global warming, and countermeasures against the problem have become urgent global necessity to protect the global environment. An emission source of CO2 is present in various fields of human activity in which fossil fuel is burned, and there is a tendency to further increase demand for suppression of the emission. Under such circumstances, intensive research on a feedstock (chemical purpose) such as urea, a boost in oil production, and a method of reducing and collecting CO2 in flue gas, and of storing collected CO2 without releasing it into the atmosphere by bringing the combustion flue gas from a boiler into contact with amine CO2 absorbing solution in a power generation facility in a thermal power plant and the like in which a large amount of fossil fuel is used, as a countermeasure to the global warming has been conducted.
As a practical method of collecting and storing CO2 in a large amount of combustion flue gas, a chemical absorption method in which the flue gas is brought into contact with CO2 absorbing solution such as an amine solution has been available. As a process of reducing and collecting CO2 from combustion flue gas using the CO2 absorbing solution, a process of bringing the combustion flue gas into contact with the CO2 absorbing solution in an absorber, and heating the absorbing solution that has absorbed CO2 in a regenerator to release CO2 and to regenerate the absorbing solution, and circulating the absorbing solution into the absorber again to be reused have been adopted (Patent Document 1).
In an operation of this conventional CO2 collecting apparatus using the chemical absorption method, the amine solution and CO2 are separated by high-temperature steam or the like, and the consumption of this steam (energy) has been required to be minimized. Therefore, a method of using two or more kinds of different CO2 absorbing solutions mixed (Patent Documents 2 and 3) and a method of improving a process of feeding an CO2 absorbing solution (Patent Document 4) have been considered.
FIG. 8 depicts a concept of a CO2 or H2S reducing apparatus in which the method of using two kinds of absorbing solutions mixed is adopted. As shown in FIG. 8, the conventional CO2 or H2S reducing apparatus 1000 includes a cooling column 1004 that cools an flue gas 1002 that includes CO2 and that is emitted from an industrial facility 1001 such as a boiler and a gas turbine with a cooling water 1003, an absorber 1006 that reduces CO2 from the flue gas 1002 by bringing the flue gas 1002 including cooled CO2 into contact with an absorbing solution 1005 that absorbs one or both of CO2 or H2S, and a regenerator 1008 that regenerates the absorbing solution 1005 by releasing CO2 from a CO2 absorbed solution (rich solution) 1007 that has absorbed CO2. In this apparatus, a regenerated absorbing solution (lean solution) 1009 from which CO2 has been reduced in the regenerator 1008 is reused as an absorbing solution. Moreover, high-reaction-speed amine 1043, water 1044, and low-reaction-speed amine 1045 are supplied to the lean solution 1009 as necessary from three storage tanks 1040, 1041, and 1042, respectively.
In the CO2 collecting method using this conventional CO2 collecting apparatus, the flue gas 1002 including CO2 is first pressured up by a flue gas blower 1010, and then, sent to the cooling column 1004 and is cooled by the cooling water 1003 to be sent to the CO2 absorber 1006.
In the CO2 absorber 1006, the flue gas 1002 countercurrent-contacts the alkanolamine-based absorbing solution 1005, CO2 in the flue gas 1002 is absorbed by the absorbing solution 1005 by a chemical reaction (R—NH2+H2O+CO2→R—NH3HCO3), and flue gas 1011 from which CO2 has been reduced is released to the outside of the system. The absorbing solution 1007 that has absorbed CO2 is also called “rich solution”. This rich solution 1007 is pressured up by a rich solution pump 1012, and is heated, in a rich/lean-solution heat exchanger 1013, by the absorbing solution (lean solution) 1009 that has been regenerated by reducing CO2 in the regenerator 1008, to be supplied to the regenerator 1008.
The rich solution 1007 discharged from an upper portion of the regenerator 1008 to the inside of the regenerator 1008 causes an endothermic reaction to release most of CO2. The absorbing solution that has released a part or most of CO2 in the regenerator 1008 is called “semi-lean solution”. This semi-lean solution becomes the regenerated absorbing solution 1009 from which CO2 has been removed substantially entirely by the time the semi-lean solution 1008 reaches a lower portion of the regenerator 1008. This absorbing solution regenerated by removing almost entire CO2 is called “lean solution”. This lean solution 1009 is heated by saturated steam 1030 in a regeneration heater 1014. On the other hand, from a top portion of the regenerator 1008, a CO2 gas 1015 combined with water vapor that has been released from the rich solution 1007 and the semi-lean solution in the regenerator 1008 is guided out. In a condenser 1016, the water vapor is condensed, water is separated in a separation drum 1017, and a CO2 gas 1018 is released to the outside of the system to be collected. Water separated in the separation drum 1017 is supplied to the upper portion of the regenerator 1008 by a condensed-water circular pump 1019. The regenerated absorbing solution (lean solution) 1009 is cooled in the rich/lean-solution heat exchanger 1013, with the rich solution 1007, is subsequently pressured up by a lean solution pump 1020, and is further cooled down by a lean solution cooler 1021, and then supplied to the absorber 1006 again, to be reused as an absorbing solution.
Reference numeral 1001a refers to a flue of the industrial facility 1001 such as a boiler and a gas turbine, reference numeral 1001b refers to a stack, and reference numeral 1031 refers steam after heat exchange. The CO2 or H2S reducing apparatus can be retrofitted to collect CO2 from an existing source of the flue gas 1002, and can be installed at the same time as the installation of a new source of the flue gas 1002. To the stack 1001b, an openable/closable door is provided, and is closed when the CO2 or H2S reducing apparatus is operating. Moreover, it is set such that the door is open when the source of the flue gas 1002 is activated but the operation of the CO2 or H2S reducing apparatus is stopped.                Patent Document 1: Japanese Patent Application Laid-open No. H7-51537        Patent Document 2: Japanese Patent Application Laid-open No. 2001-25627        Patent Document 3: Japanese Patent Application Laid-open No. 2005-254212        Patent Document 4: U.S. Pat. No. 6,800,120        